Search

Although recycled aggregate concrete (RAC) has been extensively studied, several critical problems with its fundamental behaviors still urgently need to be figured out. Therefore, this series of two reviews re-thinks fundamental behaviors of RAC based on the latest literature. In the last review (part I), the mechanical and deformation behaviors of RAC were intensively discussed. Here in part II, the relationships between the replacement ratio of recycled aggregates (RA) and the durability of RAC are further presented. It is found that, owing to the increase of total porosity, the resistance of RAC to freeze–thaw cycles, carbonation, and chloride ion penetration is usually decreased with the increasing replacement ratio of RA. As a result, the steel corrosion and corrosion-induced cracking in RAC are more serious than those in natural aggregate concrete (NAC). The prediction models for carbonation and chloride ion penetration of RAC and the corrosion-induced crack patterns are also presented. To address the degradation on the performance of RAC, several enhancement technologies such as the combined/optimisation pre-treatment on RA and fiber reinforcement are put forward. Finally, the prospects of the high-performance/efficiency methodologies and applications of RAC are also shown. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) has received huge amounts of attention in the past two decades. However, there are still many critical problems about fundamental behaviours of RAC, which need to be figured out and which otherwise limit its further sustainable popularisation. Therefore, this series of two overviews rethinks fundamental behaviours of RAC based on the latest literature. In this overview (part I), the strength development and its mechanism, as well as failure patterns of RAC under static and dynamic loading, are explored. Then, the influencing factors and prediction models of elastic modulus, shrinkage and creep of RAC are intensively discussed. It is found that, compared with natural aggregate concrete, the 28 day compressive strength of RAC is lower, whereas the long-term compressive strength of RAC may be higher, which partly depends on the strength of the parent concrete. Furthermore, because the elastic modulus of RAC is often decreased, the drying shrinkage and creep of RAC are always increased. However, the autogenous shrinkage of RAC can be decreased, and also generally develops for above 60 days. Finally, some models have been summarised to better predict the elastic modulus and long-term deformation of RAC. [ABSTRACT FROM AUTHOR]

Turning waste-to-resources is one of the key scientific interests in recent years, especially within industrial symbiosis networks in order to reduce the waste management problem and associated environmental consequences, improve materials efficiency and conserve natural resources. Considering global concern over fossil fuel burning and CO 2 emission, engineered fuels are increasingly used in cement production. The techno-environmental feasibility of using post-consumer wood derived fuel (WDF) in practical application is rarely reported. This study comprehensively evaluated the process feasibility and environmental compliances of utilizing WDF as an alternative fuel in the co-combustion process. The results revealed that physical parameters of WDF met the required fuel standards, and the air emissions by continuous emission measurements also met the specified limits and comparable to the baseline. The stack emission parameters monitored including particulates, dioxin, mercury, cadmium and thallium, and other heavy metals were about 60%, 2%, 21%, 6% and 7% of the specified limits. In addition to significantly reducing CO 2 emission (16% for using 20% WDF as co-fuel), the characteristics, of the flue gas as monitored by continuous emission monitoring and periodic stack emission at the cement plant, and the produced clinker quality were also not affected by the use of WDF. These have demonstrated the suitability of WDF as co-fuel for cement production. • Techno-environmental feasibility of bio-fuel derived from wood waste was evaluated. • Comprehensively reported the practical application of co-combustion process in the cement industry. • WDF was suitable in the co-combustion based on compliances in emission and process parameters. • About 16% reduction of GHGs emission was observed for 20% replacement of coal by WDF in the plant. [ABSTRACT FROM AUTHOR]

This study presents experimental results in an attempt to explain why photocatalytic cementitious materials prepared with white cement (WC) had superior photocatalytic NO x removal performance than those prepared with ordinary Portland cement (OPC). The UV–Vis diffuse reflectance spectra (DRS) of dry WC and OPC demonstrated that OPC had a stronger light absorption ability. And electrochemical impedance spectroscopy (EIS) analysis revealed that OPC incurred higher charge transfer resistance on the inter-surface of OPC and TiO 2 . Moreover, the OPC/P25 dry mixtures displayed a relatively lower photoluminescence (PL) intensity at 420 nm. The addition of iron oxide (Fe 2 O 3 ) in WC caused a decrease in NO x removal, a boost in light absorption, an increase in the resistance of charge transfer, and a reduction in PL intensity. Collectively, the relatively poor performance of OPC/P25 mixtures in photocatalytic NO x removal is due to a combination of stronger light absorption and lower charge separation caused by OPC. [ABSTRACT FROM AUTHOR]

Poor early-age performance (e.g. lower early strength, longer setting time) is an important technical challenge for the application of blended cementitious materials containing low reactivity or high volumes of supplementary cementing materials. In this study, the mechanism of using nanosilica (NS) to improve the early-age properties for cement mortars blended with glass powder (GP) and glass aggregates has been investigated. The results indicate that the addition of NS into glass-based cement mortar largely improved the early stiffening which was dependent on high specify surface area of the NS rather than cement hydration. Combining the use of NS and GP was conducive to compensate the delayed setting times and the strength losses caused by the incorporation of GP. These beneficial behaviors were associated with the physical, acceleration, pozzolanic and pore refinement effects of NS. In terms of heat of hydration, the inclusion of NS intensified and accelerated the appearance of the third exothermic peak (AFt to AFm) due to the absorption of sulfate ions by the increased C-S-H formation. Also, the total hydration heat liberated was found to correlate linearly with the corresponding early-age compressive strength. Microstructural analysis suggest that NS significantly helped to densify the microstructure of the GP blended cement matrix and improved the interface between the GP particle and the binder matrix. This was verified by the contribution of NS on refining the coarse pore size caused by the use of GP as a replacement of cement. [ABSTRACT FROM AUTHOR]

The management of a large amount of wood waste generated from construction activities is a challenging issue. However, wood waste is an inherently renewable resource that can be recycled and utilized for the production of green products and renewable energy. In order to minimize the environmental impacts and to provide a scientific basis for the decision-making process on the wood waste management systems, a life cycle assessment (LCA) approach was employed in this study to evaluate the potential management systems from an environmental point of view. Three alternative scenarios, including the recycling and reusing of wood waste to produce organic polymer based particleboard, cement-bonded particleboard and energy were compared with the current disposal strategy (landfill disposal), with the functional unit of 1 tonne of wood waste within a cradle-to-grave system boundary. The LCA results showed that significant reductions of environmental impacts were observed for the production of particleboard (scenario 1) and wood-cement composite (scenario 2) from wood waste compared to that of using virgin wood. However, the results also showed that scenario 3 (energy generation from bio-fuel derived from wood waste) was the best strategy, as this technology reduces more than 1 tonne of CO 2 eq greenhouse gases compared to the energy generation from coal. The analysis conducted in this study can serve as guidelines to design a sustainable and resource-efficient wood waste management system. [ABSTRACT FROM AUTHOR]

In order to reduce the leaching of pollutants and remove the Al and Zn/Al alloy from municipal solid waste incineration bottom ash (MSWIBA), an optimized alkaline pre-treatment procedure was developed in this study. The influences of alkaline conditions on the removal rate of Al and Zn/Al alloy were investigated, including [OH] − concentration, temperature, particle size, liquid/solid ratio and treatment duration. The experimental results showed that the optimized alkaline pre-treatment conditions to efficiently remove the Al and Zn/Al alloy was by using a minimum of 1.0 mol/l [OH] − , at 55 °C and with a minimal liquid/solid ratio of 5. The removal rate of Al and Zn/Al alloy followed an S-shape curve, in which the slow beginning stage was attributed to the protection of the oxidation layer and the quenched product around the Al and Al/Zn alloy. After 3 h of the optimized alkaline pre-treatment, the leaching of Cr, Cu, Pb and Zn of the treated MSWIBA was reduced by more than 90% of that of the original MSWIBA. The alkali-silica reaction test further indicated that the expansion of concrete prepared with the pre-treated MSWIBA was significantly reduced and there was no macro-crack or spalling damage on the surface of the tested specimens. [ABSTRACT FROM AUTHOR]

As the world’s most widely used construction material, the production of concrete has been recognized to lead to major environmental impacts. To promote sustainability in the concrete industry, various kinds of supplementary cementitious materials (SCMs), such as fly ash, blast furnace slag and silica fume have been used to replace cement in concrete production. The nature of these SCMs has therefore been changed from wastes to co-products or by-products. Life cycle assessment (LCA) has been increasingly adopted in the concrete industry to assess environmental sustainability. However, the choice of an appropriate method for impact distribution in the LCA of concrete incorporating SCMs is a research challenge. This study aimed to present a comprehensive review of the impact allocation approaches for assessing the environmental impacts of SCMs-incorporated concrete. Furthermore, the use of the system expansion approach was compared with the conventional mass and economic allocation approaches. A case study of concrete production using SCMs in Hong Kong was conducted using the different approaches. The results were then analyzed and it was concluded that the system expansion approach is appropriate for the assessment of the environmental impacts of SCMs-incorporated concrete. [ABSTRACT FROM AUTHOR]

The water resistance of magnesium oxychloride cement (MOC) incorporating glass powder (GP) and pulverized fuel ash (PFA) with and without CO 2 curing was investigated in terms of the strength retention coefficient and the volume stability. The microstructure was studied using quantitative X-ray diffraction (QXRD), thermogravimetry (TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the effect of incorporating GP on the water resistance is much lower than that of PFA due to the lower pozzolanic activity of GP generating a lower amount of magnesium silica hydrate gel (M-S-H gel). The MOC incorporated with GP or PFA showed high water resistance after CO 2 curing due to the higher quantity of amorphous gel that formed a much denser interlocking network. [ABSTRACT FROM AUTHOR]

This paper presents a study on alkali activated cement (AAC) mortar produced with waste soda-lime-silica glass. The waste glass was used simultaneously as a precursor and fine aggregates in the alkali activated fly ash-slag mortar. The influences of waste glass in cullet and powder forms on workability, compressive and flexural strengths, fire resistance of the AAC mortar were investigated. The experimental results showed that the workability was gradually increased as the replacement level of natural sand by glass cullet was increased, and it was significantly improved with decreasing aggregates-to-binder ratios. The mechanical properties data indicated that the compressive strength was reduced as the glass cullet content increased. However, for the flexural strength, the optimum percentage of glass cullet replacement was 50%. Due to the low reactivity, a reduction in strength was observed when the glass powder was used to replace the fly ash and slag. Nevertheless, in terms of fire resistance, the incorporation of glass cullet could improve the resistance of the AAC to high temperature exposures (800 °C). In particular, the AAC mortar prepared with the glass powder as a precursor exhibited remarkable resistance to high temperature. The use of waste glass in AAC material was feasible from the mechanical properties and fire resistance points of view. [ABSTRACT FROM AUTHOR]

This study aimed to develop an effective surface pre-treatment method for recycled rubber particles to improve the sound insulation properties of rubberized lightweight aggregate concrete. In this study, the control lightweight aggregate concrete mixture was prepared using lightweight expand clay aggregate as the coarse aggregate and furnace bottom ash (FBA) as the fine aggregate. The results showed that when all the FBA was replaced by the recycled rubber aggregate, the overall sound reduction level was 32.5 dB (A), which was already significantly higher than the 15.5 dB (A) achieved by the control concrete mixture prepared without rubber aggregates. A simple cement slurry coating pre-treatment method was developed to modify the surface of the recycled rubber aggregate. 10.9 dB (A) and 14.8 dB (A) further noise reduction were achieved when FBA was replaced by 50% and 75% of the pre-treated rubber aggregates, respectively. The dynamic Young's Modulus of the concrete mixtures was tested and the surface bonding of the concrete mixtures prepared with the pre-treated/un-treated rubber aggregate was also investigated. The results suggested that the pre-treatment method resulted in weaker bonding between the rubber aggregates and the cement paste, and thus increased the vibration absorption capacity and enhanced the noise insulation properties of the concrete. [ABSTRACT FROM AUTHOR]

Sewage sludge ash (SSA) is the byproduct obtained from incinerating mechanically dewatered sewage sludge. Some published literature mentions that mortars of comparable strength can be produced using a small amount of SSA to replace cement. However, information on how SSA affects the properties of cement mortars is limited given the pozzolanic activities of most SSA being modest. This study identified the mechanisms behind some beneficial effects of the SSA on the strength development of mortars through a comparison study with fine sewage sludge ash (FSSA) and pulverized fly ash (PFA). The findings of this study indicated that the presence of SSA accelerates the rate of heat evolution from cement hydration while PFA does not produce this effect. A higher content of SSA or FSSA produces a greater effect. Replacing cement by SSA or FSSA up to 10% did not induce significant changes to the pore structure of the pastes. The formation of brushite in SSA or FSSA cement mortars contributes to the long-term strength of the mortars. PFA reduces the drying shrinkage of the mortars, but SSA causes greater drying shrinkage due to increasing content of mesopores with sizes less than 0.025 µm. This harmful effect is greater with FSSA. [ABSTRACT FROM AUTHOR]

Adopting accelerated carbonation technique is one of ways to improve the properties of recycled coarse aggregate (RCA). In this study, the uni-axial dynamic compressive behavior of recycled aggregate concrete (RAC) and RAC with carbonated RCA (CRAC) was experimentally investigated when the strain rates were between 10 −5 /s and 10 −1 /s. The strain-rate sensitivities of RAC and CRAC were evaluated from the effect of strain rate on stress-strain curve, peak stress, peak strain, ultimate strain, elastic modulus, energy absorption capacity and failure pattern. The results showed that the uni-axial compressive stress-strain curves given in the Chinese code agreed well with the experimental results. As the strain rate was increased, the peak stress, elastic modulus and energy absorption capacity showed an increasing trend for both RAC and CRAC. The peak stress and elastic modulus of CRAC were higher than that of RAC. The strain-rate sensitivity of peak stress and elastic modulus of CRAC was less obvious than that of RAC, which may be explained from Stefan effect and strain-rate sensitivity of crack propagation resistance. [ABSTRACT FROM AUTHOR]

In recent years, recycled waste materials have been widely used to produce construction materials in an effort to reduce the utilization of natural resources and post-consumer wastes entering landfills. In this paper, the results of an experimental programme on studying the feasible use of spent fluorescent glass (FG) as a fine aggregate replacement in cement mortar are presented. Two types of FG were adopted in this study, one with (FG-A) and one without (FG-B) heating treatment at around 375 °C, to ensure the removal of mercury within the broken FG. The use of FG up to 40% to replace sand showed no obvious difference in density, but demonstrated an enhancement in workability and less shrinkage in the cement mortar. In comparison, the reduction of mechanical strength for a given content of FG-A usage in mortar is relatively lower than that of FG-B. This could be due to the FG-A (after the heating treatment) being free from the organic lacquer and the smooth coating, resulting in a better bond with the cement paste matrix. All the FG samples experienced big length changes due to the alkali-silica reaction (ASR), associated with their high solubility and the original microcracks present in the interior of the thin FG particles. The Toxicity Characteristic Leaching Procedure (TCLP) results indicated that utilizing of both FG-A and FG-B in the cement mortar could effectively reduce the leachability of mercury, from 12.99 mg/L and 70.55 mg/L (determined original FG-A and FG-B values before they were incorporated into the cement mortar) to below the permissible limit of 0.5 mg/L. However, the replacement ratio of FG should be limited to 30% or below. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of corrosion degree and corrosion morphology on the mechanical properties of the steel reinforcement. Tensile tests were first conducted on the steel reinforcement corroded by long-term (26–28 years) exposures to a chloride-rich natural environment. Through the tests, besides the corrosion degree, which was the most often used parameter to assess the corrosion, the corrosion morphology (i.e. represented by the radius of gyration of the residual cross-section) was found to be a very important factor influencing the ductility of the steel reinforcement and three typical corrosion morphologies were identified. Afterwards, tensile tests on a series of steel reinforcement artificially made with the above three types of corrosion morphologies, which were simulated through mechanically induced cross-sectional losses, were conducted with the aim of quantifying the relationship between the ductility of the corroded reinforcement and the corrosion degree and morphology. It was found that, for all the corrosion morphologies, that the ultimate strain of the corroded steel reinforcement was reduced in an exponential manner with the corrosion degree up to a critical level (30% by mass loss), beyond which it then stayed stable. However, different corrosion morphologies led to significantly different degradation rates with the corrosion degree. A model was proposed to describe the above relationships and validated through comparisons with test results on both the artificially simulated and the naturally corroded steel reinforcement. [ABSTRACT FROM AUTHOR]

With the rapid advances of the electronic industry, the management of the cathode ray tube (CRT) glass waste has become a major environmental problem. In this study, the CRT funnel glass sand untreated with nitric acid (n-TFG) and treated with nitric acid (TFG) were used to replace river sand as fine aggregate for the production of the mortar. The TFG glass sand series mortars exhibit the worse fluidity and fluidity preservation, the shorter setting times, the lower wet density and mechanical properties than those with n-TFG glass sand. The use of TFG glass sand in the mortar also results in the lower drying shrinkage, alkali-silica reaction (ASR) expansion and leaching content of lead than the blended n-TFG glass sand mortars. Moreover, at the drying shrinkage period of 56 days, the drying shrinkage values of the mortars with TFG glass sand are within the limit of 0.075%. The mortars prepared by TFG glass sand have a low ASR expansion, at the tested age of 14 days, which are below permissible limits (0.10%). The lead leaching of the mortars with TFG glass sand comply with the regulatory limits. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the water resistance of magnesium oxychloride cement (MOC) incorporating incinerated sewage sludge ash (ISSA). Cement pastes were prepared to evaluate the compressive strength and microstructure of the blended cements. Besides, the volume stability of cement mixture during air curing and water immersion was tested by measuring the length change of mortar bar specimens. In addition to cement paste and mortar, Na 2 SiO 3 ·9H 2 O and Al(NO 3 ) 3 ·9H 2 O were used to react with MOC as the replacement of ISSA to synthesize pure hydration products. Paste studies revealed that ISSA additions of 10–30% significantly improve the water resistance of MOC. Mortar studies showed that ISSA significantly reduced expansion of mortar bars immersed in water. The improved water resistance and reduced expansion is directly related to the decrease in MgO content of pastes and an improved stability of Phase 3 (3Mg(OH) 2 ·MgCl 2 ·8H 2 O) and Phase 5 (5Mg(OH) 2 ·MgCl 2 ·8H 2 O) in water. Results from sol-gel experiments suggest that ISSA can act as a source of soluble Al and Si which results in the formation of an amorphous M-Cl-A-S-H type cementitious gel. The gel formed could help improve Phase 3 and Phase 5 stability in water by interlocking mechanisms which impede the access of water to Phase 3 and Phase 5. [ABSTRACT FROM AUTHOR]

For alkali-activated slag cement (AAC), an environmentally-friendly material, high-alkalinity activators are normally utilized for activation, which can lead to possible concrete degradation owing to alkali-silica reaction (ASR) when alkali-active aggregates were used. This study explored the effectiveness of lightweight aggregates in mitigating ASR behaviors of the AAC system. Alkali-reactive expanded perlite and non-alkali-reactive expanded shale were used as lightweight aggregates to compare ASR behaviors in ordinary Portland cement (OPC) and AAC systems. The formation of ASR gel in the expanded perlite was expansive, whereas the higher Ca/Si ratio calcium-aluminate-silicate-hydrate (C-A-S-H) in the non-alkali-reactive expanded shale did not cause expansion. In contrast with the OPC system, the larger amount of lower Ca/Si ratio ASR gel caused more deleterious ASR expansion and cracks in the AAC system. Furthermore, replacing expanded perlite with expanded shale effectively mitigated the ASR expansion. Discussion on the ASR mitigation mechanism of lightweight aggregates was provided for predicting the influence on the concrete. [ABSTRACT FROM AUTHOR]

The safe treatment of marine sediment has been a global-scale challenge. To reduce the environmental impacts associated with Portland cement (PC), an environment-friendly binder consisting of quicklime and ground granulated blast-furnace slag (GGBS) was used in the stabilization/solidification of natural marine sediment. Although the combination of lime and GGBS is used to stabilize the sediment with very low water content or moderate water content in previous studies, the natural marine sediment with such a high water content has not been treated by the quicklime–GGBS binder up to now. Therefore, a series of tests were performed to study the physicochemical, mechanical, and microstructural characteristics of quicklime–GGBS stabilized sediments. The results indicated that the quicklime–GGBS solidified/stabilized sediment had a similarly low water content at a proper quicklime-binder ratio to that of PC-stabilized sediments. The pH of quicklime–GGBS solidified sediments gradually decreased as the quicklime-binder ratio decreased and the curing period increased. The unconfined compressive strength (UCS) of quicklime–GGBS stabilized sediments was 1.4 times higher than that of the corresponding PC-stabilized sediments using the same test conditions. The hydration products effectively bonded the sediment particles and filled the pores between the sediment particles, facilitating the improvement of the UCS of the quicklime–GGBS stabilized sediment. The findings indicated that the use of GGBS and a small amount of quicklime can replace PC to stabilize natural marine sediment with high water content. This would be to provide binder dosage and component proportion for the field application of quicklime–GGBS binder and to significantly improve the economical and environmental effects of the treatment of high water content sediment. Innovative lime-activated GGBS is used as a binder in the improvement of sediment with ultrahigh water content. The water content, pH, and UCS of lime–GGBS stabilized sediments are contrastively studied. The engineering performances of lime-GGBS stabilized sediments are better than those of PC-stabilized sediment. An optimal and appropriate lime-binder ratio is suggested. Microstructure mechanism of lime–GGBS stabilized sediment is revealed through series of micro-tests. [ABSTRACT FROM AUTHOR]

The current work scrutinizes the effectuation of seawater on morphological properties, pore structure, and compressive strength during the hydration process of fly ash blended cement at 3, 7, 28, 56, and 90 days to better understand the influence of salinity conditions of seawater on the microstructural modification and strength development of the hydration products as well as the total porosity. The chemical reaction's mechanism of mightily soluble salts, for example, Mg2SO4 and NaCl, with hydrated fly ash and blended cement (calcium‐bearing phases) was also confirmed. Fourier‐transform infrared spectroscopy has been appointed to observe and characterize the energetics of variation in the formulation of portlandite (CH), calcium silicate hydrate, gypsum (Gy), ettringite (AFt), and calcium chloroaluminate (Friedel's salt [FS]) throughout the hydration process of fly ash blended cement with seawater in comparison with deionized water. X‐ray diffraction analysis exposed that the peak intensities of FS, portlandite, and some particular phases of the hydrated fly ash blended cement in seawater are higher and sharper than the comparable peaks in deionized water. Mercury intrusion porosimetry‐measurements have been appointed that the total porosity of artificial seawater (ASW) was decreased from 28.9% at 3 days to 19.4% at 56 days. In addition, the average, median, and critical pore diameter were decreased in ASW while compared to deionized water (DIW). The reaction products of this work were also characterized using scanning electron microscopy, EDS, compressive strength, and isothermal calorimeter. [ABSTRACT FROM AUTHOR]

This paper presents a study on the use of pulverized fuel ash (PFA) to improve the water resistance of magnesium oxychloride cement (MOC). Strength retention coefficients and volume stability were tested to evaluate the water resistance of MOC, in which the addition of PFA resulted in a remarkable improvement. The characterization of hydration products before and after water immersion was carried out using quantitative X-ray diffraction (QXRD), thermogravimetric (TG), Fourier-transformed infrared spectroscopy (FTIR) and scanning electron microscope (SEM). With the Q-XRD analysis, it was shown that the addition of PFA could result in the great increase of the amount of amorphous phase during air curing. This amorphous gel was identified as a mixture of magnesium-chloride-silicate-hydrate gel (M-Cl-S-H gel) and magnesium-chloride-hydrate gel (M-Cl-H gel) by elemental mapping scanning. It suggested that PFA could not only react with MOC to form M-Cl-S-H gel, but also change the morphology of magnesium oxychloride. The generation of insoluble M-Cl-S-H gel and M-Cl-H gel and densification of the microstructure contributed to the improvement of the water resistance of MOC. The MOC mortar expanded during air curing due to the hydration of excess MgO. Water immersion led to more expansion of MOC mortar as a result of the continuously hydration of excess MgO and the formation of Mg(OH) 2 . Adding PFA could increase the expansion of MOC mortar during air curing, which may because the amorphous gel could remain more water and benefit to the hydration of MgO. While, the addition of PFA could decrease the expansion of cement mortar during water immersion perhaps due to the reduction of the content of excess MgO and the insoluble amorphous-gel-layer that protect the MgO from hydration. Moreover, CO 2 curing could further improve the performance of the PFA-blended MOC due to the formation of a higher content of amorphous gel. [ABSTRACT FROM AUTHOR]

The proper treatment of lead (Pb) contaminated soils and incinerated sewage sludge ash (ISSA) has become an environmental concern. In this study, ordinary Portland cement (OPC) and blended OPC containing incinerated sewage sludge ash (ISSA) were used to solidify/stabilize (S/S) soils contaminated with different concentrations of Pb. After curing for 7 and 28 d, the S/S soils were subjected to a series of strength, leaching and microscopic tests. The results showed that replacement of OPC by ISSA significantly reduced the unconfined compressive strength (UCS) of S/S soils and leached Pb. In addition, the leaching of Pb from the monolithic samples was diffusion controlled, and increasing the ISSA addition in the samples led to a lower diffusion coefficient and thus an increase in the feasibility for “controlled utilization” of S/S soils. Furthermore, the proposed S/S method significantly decreased the amount of Pb associated with carbonates and increased the amount of organic and residual Pb in S/S soils, reflecting that the risk of Pb contaminated soils can be effectively mitigated by the incorporating of ISSA. Overall, the leachability of Pb was controlled by the combined effect of adsorption, encapsulation or precipitation in the S/S soils. [ABSTRACT FROM AUTHOR]

Red mud is a waste material derived from alumina refineries through the Bayer process. In this paper, the red mud is used to replace fly ash at various replacement ratios in the production of self-compacting mortars. Two series of mix proportions (series I and II) are designed to investigate the fresh and hardened properties of self-compacting mortars (SCM). In series I, the replacement ratios of red mud range from 0% to 50% by weight; in series II fly ash is replaced by red mud at 0%, 25%, 50%, 75% and 100% by weight. The results show that the fluidity is reduced as red mud is used to replace fly ash; meanwhile, a trend towards mitigation of bleeding is observed due to red mud porosity. An increase in red mud content also brings a slight decrease of hardened density, an increase of water absorption and permeable voids. In the case of mechanical properties, red mud is effective in enhancement of the compressive and flexural strength; the compressive and flexural strength of SCM mixture samples prepared with red mud at 50% of replacement ratio are higher than those of other samples. As for the drying shrinkage and autogenous strains, all drying shrinkage values are increased as red mud is used to replace fly ash; however, a decrease of autogenous strains is observed with an addition of red mud, and the trend is more pronounced when the replacement ratio is 50%. [ABSTRACT FROM AUTHOR]

In order to enhance the CO 2 curing efficiency of concrete block prepared with recycled aggregates, several material characteristics of the concrete block including moisture content, bulk density, aggregate to cement ratio, recycled aggregate content and types of binders, were studied experimentally to assess their effects on the CO 2 curing process. The results indicated that, during 2 h of CO 2 curing period, the moisture content and aggregate to cement ratio of the prepared blocks had significant effects on the CO 2 curing degree and the compressive strength. Appropriate pre-drying of the block specimens before CO 2 curing enabled the maximum curing degree, and the compressive strength attained was comparable or superior to that of the 6 h steam cured blocks. The bulk density and recycled aggregate content of the prepared blocks would also influence the CO 2 curing degree, but their effects on compressive strength were more complex. It was confirmed that the presence of recycled aggregate in the concrete blocks can promote the CO 2 curing efficiency. [ABSTRACT FROM AUTHOR]

Red mud derived from alumina refineries through the Bayer process is a waste material with a density of 2187 kg/m 3 . The particle size distribution of the red mud is similar to fly ash. In this paper, the physical and chemical properties of the red mud including oxide and mineral contents are studied by XRF and XRD. The potential use of the red mud as a pozzolanic material to replace fly ash in self-compacting concrete (SCC) is assessed by conducting a range of fresh and hardened properties test (such as slump flow, density, porosity, compressive strength, splitting tensile strength, elasticity modulus and drying shrinkage). The XRF and XRD results show that the oxide forms in the red mud are mainly SiO 2 , Al 2 O 3 and CaO at 45.76%, 40.69% and 4.98% respectively, and the crystalline phases are mainly gismondine, goosecrekite and epistilbite which belong to the zeolite family. The results show that the strength activity indeces (SAI) of the red mud are 79.60 and 88.46 at 7 days and 28 days respectively, which are approximately equal to that of a common Class F fly ash. Meanwhile, with the use of the red mud to replace fly ash in SCC, the compressive strength, splitting tensile strength and elasticity modulus are enhanced. Moreover, with the addition of the red mud, the drying shrinkage decrement is observed in SCC, which might be due to the red mud's internal curing. Therefore, the feasibility of utilizing the Bayer red mud in SCC is demonstrated. [ABSTRACT FROM AUTHOR]

With an increasing interest in recycling and reusing waste, there is a need to carry out research on exploring ways to transform industrial wastes into construction materials. This paper attempts to explore the feasibility of reutilizing textile effluent sludge (TES) for producing concrete blocks with a pretreatment step. The lime-based pretreatment process was adopted to remove ammonia in TES which had been found to lead to bad odor and strength loss of the concrete blocks. The concrete blocks were prepared with an aggregate to cement ratio of 12, 10 and 6. The pretreated TES was adopted to replace the fine aggregate at a mass ratio ranging from 0% to 30%. The compressive strength and drying shrinkage values were determined to evaluate the performance of concrete blocks containing TES. The results indicated that the lime-based pretreatment process can lower the ammonia concentration in TES significantly. The concrete blocks with a lower TES content and lower ammonia concentration had higher compressive strength and better volume stability. When the TES content in the concrete blocks was about 10%, the concrete blocks with an aggregate to cement ratio of 10 can satisfy the minimum strength requirement for non-load bearing applications. Meanwhile, the result of leaching test indicated that the toxic trace metals present in textile effluent sludge could be stabilized/solidified and metal leaching from the concrete blocks is not a concern. [ABSTRACT FROM AUTHOR]

The influence brought by Furnace Bottom Ash (FBA) incorporation on the properties of lightweight aggregate concrete was studied systematically. In total, six mixtures of concrete targeted at a 28 d compressive strength of 30 MPa were designed, including one control mix made with all normal weight aggregates and at a water/cement ratio (w/c) of 0.6, and another five lightweight aggregate concrete mixes at a w/c of 0.39 by using 0, 25%, 50%, 75% and 100% FBA replacing natural fine aggregate (crushed fine stone). The testing results of the hardened concrete properties showed that, for the lightweight aggregate concrete using 100% FBA to replace crushed fine stone, a 28 d oven-dried density of about 1500 kg/m 3 was obtained. The test results showed the lightweight aggregate concrete had lower strength and stiffness compared to the normal aggregate concrete. But in terms of the effectiveness of strength provided by unit weight of concrete indicated by compressive strength in MPa divided by saturated-surface dried (SSD) density in g/cm 3 , f c /D, a satisfactory ratio can be obtained when not more than 50% FBA was used to replace the crushed fine stone. The durability property indicated by the chloride ion penetration test shows the lightweight aggregate concrete with FBA had high chloride ion penetrability. The heat insulation property (thermal conductivity K-value) test demonstrated that by using the porous lightweight aggregate, the thermal conductivity could be lowered to around 70% of the control. When more FBA was used to replace crushed fine stone, the thermal conductivity value could be further reduced. The results of this study demonstrated it is feasible to produce lightweight aggregate concrete with high volume of FBA incorporation for building insulation uses. [ABSTRACT FROM AUTHOR]

Abstrac1t This paper presents the experimental results of a study on the effect of the quality of parent concrete (PC) on the properties of recycled aggregates (RAs) that are derived from them, and on the mechanical and durability properties of normal strength and high performance recycled aggregate concrete (NSRAC and HPRAC). PC with strength grades ranging from 30 to 100 MPa was crushed to the size of coarse aggregates (<20 mm), and then used to produce new NSRAC and HPRAC mixes. The results indicated that the compressive strength of the NSRAC and HPRAC prepared with RA derived from 80 and 100 MPa PCs was similar or slightly higher than that of natural aggregate concrete. Moreover, the concrete mixtures made with RA are derived from parent concrete with higher strength had lower drying shrinkage and higher resistance to chloride ion penetration. The RA derived from 80 and 100 MPa PCs can be used to replace 100% natural aggregates for the production of high performance concrete. [ABSTRACT FROM AUTHOR]

The use of 100% recycled glass as aggregates in architectural mortar is regarded as an environmentally friendly, cost-effective and attractive feature for construction applications due to the natural characteristics of glass (e.g. aesthetic pleasing, impermeability, chemical resistance properties). However, the need to use large quantities of white cement for architectural products may increase the overall cost of production. Therefore, the possibility of using a near-white coloured ground granulated blast furnace slag (GGBS) to replace white cement for architectural mortar production is an attractive option. This paper reports a study which is an extension of our previous work aiming to investigate the feasibility of using large volumes of GGBS (ranging from 15% to 75% white cement replacements) to produce self-compacting-based architectural mortars. To improve the appearance (whiteness) of the mortar, a small quantity of titanium dioxide (TiO2) was added to the selected mixes for comparison purposes. Fresh and hardened properties of the mortar including mini-slump flow, density, water absorption, flexural strength, equivalent compressive strength, drying shrinkage, alkali silica reaction (ASR) and acid attack resistance were investigated. The overall performance showed that it is feasible to use GGBS for the production of architectural mortar and 60% replacement of white cement by GGBS was determined to be optimal. The replacement significantly increased the flexural strength, and reduced the drying shrinkage and risk of ASR expansion, as well as improved the ability to resist acid attack of the mortar produced. [ABSTRACT FROM AUTHOR]

In this paper, the effects of high temperature exposure of recycled aggregate concretes in terms of residual strengths, capillary water absorption capacity and pore size distribution are discussed. Two mineral admixtures, fly ash (FA) and ground granulated blast furnace (GGBS) were used in the experiment to partially replace ordinary Portland cement for concrete production. The water to cementitious materials ratio was maintained at 0.50 for all the concrete mixes. The replacement levels of natural aggregates by recycled aggregates were at 0%, 50% and 100%. The concretes were exposed separately to 300°C, 500°C and 800°C, and the compressive and splitting tensile strength, capillary water coefficient, porosity and pore size distribution were determined before and after the exposure to the high temperatures. The results show that the concretes made with recycled aggregates suffered less deteriorations in mechanical and durability properties than the concrete made with natural aggregates after the high temperature exposures. [ABSTRACT FROM AUTHOR]

Steel corrosion caused by chloride penetration is an important problem in construction practices threatening the long-term durability of reinforced concrete structures. In this study, the effects of blast-furnace slag on the passivation and corrosion processes of carbon steel embedded in cement pastes were investigated by electrochemical measurements, and equivalent circuit models were proposed for analysis of the passivation and corrosion processes. The spatial chloride distributions in the cement paste after corrosion initiation were determined distinguishing between amounts of total, free and bound chloride. The values of the open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements indicated that the carbon steel embedded in cement pastes was passivated due to the presence of an alkaline pore solution. However, the formation of passive layers on the surface of carbon steel in the slag-blended cement paste was weakened by the more negative OCP value due to a lower pH value and higher sulphide concentration in the pore solution. Upon initiation of corrosion during the electrical acceleration test, the OCP value dropped to a significantly more negative value whereas the Warburg impedance in the equivalent circuit model sharply decreased. Moreover, the addition of slag decreased the threshold chloride concentration at the steel surface to initiate steel corrosion. On the other hand, the enhanced resistance against chloride penetration and the higher chloride binding capacity resulted in an overall increase of the corrosion resistance of carbon steel in slag-blended cement paste. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of different pretreatments on the properties of MSWIFA were studied. • Emission of NH 3 (gas), apart from H 2 (gas), was detected during the washing process. • A set of system for collecting H 2 (gas) and NH 3 (gas) was devised. • Pretreatments reduced the leaching toxicities of MSWIFA and removed anions. • Pretreatments enhanced the pozzolanic activity of MSWIFA. Swelling caused by gas generated from municipal solid waste incineration fly ash (MSWIFA) when it is mixed with alkali limits its uses. Besides, the leaching of anion salts and heavy metals contained in MSWIFA poses a high risk to environment. This study presents the feasibility of a one-step alkaline washing, one-step thermal quenching and two-step combination of alkaline washing and thermal quenching pretreatment methods in altering the key properties of MSWIFA for promoting its reusability. It was found that apart from H 2 (gas), NH 3 (gas) was also generated during the alkaline washing of the MSWIFA. Besides, pretreatments led to the reduction in particle size, the increase in pore volume and specific surface area of the MSWIFA, as well as the removal of chloride and sulfate anions. All the pretreatment methods were effective in reducing leaching of heavy metals to below levels of nonhazardous waste except Cd and Pb with alkaline washing. Furthermore, both the chemical Frattini test and the mechanical activity index test showed improvement in pozzolanic activities of the MSWIFA after the pretreatments. Overall, the combined pretreatment method was most effective in eliminating gas emission, and reducing leaching of metal ions and anions from the ash, while enhancing the pozzolanic activity of the ash. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the experimental results of a study on comparing the difference in properties of recycled aggregates (RAs) with varying amounts of old adhered mortar obtained from different sources and evaluating the influence of the different RAs on the mechanical and durability properties of recycled aggregate concrete (RAC). Four concrete mixes (one with natural aggregate and three others with recycled aggregates) with 28 day target compressive strength varying from 30 MPa to 80 MPa are designed by using each RA to fully replace NA. The properties of RAC are also modeled by using the artificial neural networks (ANN) method. The experimental results show that the performance of RAs from different sources varied greatly and RA of good quality can be used to produce high strength concrete with hardened properties comparable to those of the corresponding natural aggregate concrete (NAC). The comparison of the predicted results based on the ANN models and the experimental values indicated that the ANN method could be used to evaluate the properties of RAC made with RAs derived from different sources. This will facilitate the wider application of RA in concrete. [Copyright &y& Elsevier]

Abstract: This paper investigates the feasibility of using recycled glass derived from discarded cathode ray tube (CRT) glass as an alternate fine aggregate for the production of dry-mixed concrete paving blocks. The recycled CRT funnel glass used had been acid treated and regarded as a non hazardous material based on the regulatory thresholds of the Toxicity Characteristic Leaching Procedure (TCLP). Two series of concrete paving blocks were prepared, one with and one without the use of coarse aggregate. Additionally, TiO2, a photo-catalyst was added to the surface layer of the blocks during the fabrication process to effect photo-catalytic reaction for the removal of an air pollutant, nitrogen oxide (NO). For each series, the CRT glass was used to replace the fine aggregate by volume at different ratios. Their physical, mechanical and durability properties, lead leachability, and photocatalytic air purifier performance were studied. The results show that the use of up to 100% CRT funnel glass as fine aggregate in concrete paving blocks not only have satisfactory levels in compressive strength (>45 MPa) and ASR expansion (<0.1%), but improved the resistance to water absorption, drying shrinkage and photocatalytic performance for reducing air pollutants. However, the TCLP results reveal that the casting method of producing dry-mixed concrete blocks had a significant influence on lead leaching, and the replacement ratio of the CRT glass should be limited to about 25%. [Copyright &y& Elsevier]

Highlights: [•] This paper reviews the feasibility of using PCM in concrete. [•] There are generally three probable means of PCM incorporation in concrete. [•] The three predominant are immersion, impregnation and direct mixing. [•] Method of PCM incorporation has a great influence on the properties of concrete. [•] The influence on the fresh, mechanical and thermal properties is reviewed. [Copyright &y& Elsevier]

• Utilizing T-CRTF glass sand enhances density, mechanical strength, drying shrinkage. • High-amount T-CRTF glass mortar has low water absorption, chloride ion penetration. • Mortar with 75 % T-CRTF glass sand has the highest ASR expansion. • Lead in 75 % T-CRTF glass sand mortars is easily to release into the environment. • Sustainable mortar can be prepared by recycling 50 % T-CRTF glass sand in FA mortar. Utilizing acid treated CRT funnel (T-CRTF) glass sand in mortar is a feasible option to lower natural resource consumption and protect the environment. In this study, T-CRTF glass sand replaces river sand in mortar at four levels (0, 25 %, 50 %, 75 %). The inclusion of T-CRTF glass sand improves the fluidity properties of mortar. At the initial curing period (3 days), T-CRTF glass sand mortar exhibits the larger hardened density, mechanical strength than river sand-based mortar. After all mortars cured in water for 90 days, the hardened densities and the mechanical strength of mortars with 25 %, 50 % T-CRTF glass sand are the slightly higher than control mortar. The use of the excessive T-CRTF glass sand can no increase anyway the long-term hardened density and mechanical strength of mortars. The recycle of T-CRTF glass sand to mortars reduces the water absorption, the chloride ion penetration, enhances the drying shrinkage, the alkali-silica reaction (ASR) expansion and the lead leaching amount. FA, GGBS mortars with 75 % T-CRTF glass sand have the lowest water absorption, chloride ion penetration in all mortars. The introduction of large amount T-CRTF glass sand to FA, GGBS mortars is more easily to induce the drying shrinkage, the ASR expansion and the long-term lead leaching from mortar. Considerations from the long- term mechanical strength, durability behaviors and environmental compatibility of mortar mixture, the application of 50 % T-CRTF glass sand in FA mortar is the sustainable method to dispose CRT funnel glass. [ABSTRACT FROM AUTHOR]

This study aimed at developing sewage sludge ash (SSA) as a green binding material through geopolymerization for saving natural resources and reducing problems with the waste disposal. Geopolymer pastes based on a precursor comprising 25 wt% of metakaolin (MK) and 75 wt% of SSA were synthesized using the dry-mixed method. Compressive strength tests of the specimens revealed that geopolymers produced from mixes with a Na 2 O/SiO 2 molar ratio of 0.30 and a SiO 2 /Al 2 O 3 molar ratio in the range of 3.00 to 3.60 achieved the highest compressive strength after 28 days of curing, regardless of temperature. The microstructural analyses showed the formation of N-A-S-H gels in the specimens. The initial curing temperature had a significant influence on the compressive strength of the geopolymers. Specimens initially cured at 40 °C for 7 days and then stored at room temperature showed progressive gain in compressive strength with time. However, raising the initial curing temperature from 40 °C to 60 °C resulted in the formation of cracks in the matrix and new mineral of zeolite P (Na) which caused a notable loss of late-age strength. Leaching toxicity tests showed that the concentrations of heavy metal(loid)s in leachates did not exceed the specified limits. [Display omitted] • Sewage sludge ash/metakaolin geopolymers were synthesized by the dry-mixed method. • Microstructural analyses proved the formation of geopolymer gels. • The optimal Na 2 O/SiO 2 and SiO 2 /Al 2 O 3 molar ratios were identified. • Strength improvement was achieved at 40 °C. • Further rise in the initial curing temperature generated zeolite crystallites and crack features. [ABSTRACT FROM AUTHOR]

Abstract: The rapid advance in the electronics industry has led to the disposal problem related to the cathode ray tube (CRT) glass waste. In this study, the Ordinary Portland cement (OPC) of 15% was replaced by fly ash to mitigate the potential of alkali–silica reaction (ASR) expansion, the crushed nitric acid-treated CRT funnel glass sand (TCF) was used to replace river sand fine aggregate of 0%, 25%, 50%, 75% in the high-density concrete. The fresh, mechanical properties of the high-density concrete containing TCF glass sand were studied, the alkali–silica reaction (ASR) of the mortar and drying shrinkage of the concrete were also evaluated. The test results showed that the use of TCF glass sand improved the fresh properties of the concrete, but reduced the mechanical properties of the concrete. Furthermore, at the drying period of 56 days, all concrete mixtures had an acceptable drying shrinkage value below 0.075%. ASR expansion values of the mortar with TCF glass sand were found to be below the limit of 0.1% at tested age of 14 days. Preliminary results obtained from this study had demonstrated that the CRT funnel glass (an original hazardous material) can be treated, processed and reutilized for the production of the high-density concrete. [Copyright &y& Elsevier]

Abstract: A novel polymer concrete (PC) was synthesized by mixing epoxy resins and waste glass as aggregates. In this study, metakaolin (MK) and fly ash (FA) were used as filler and compositions with 0%, 10% and 15% by weight of recycled glass sand (<2.36mm) were prepared to investigate the mechanical and durability properties of the PC. The results indicated that all compositions assessed in this study display high strength and modulus of elasticity values. MK and FA have a significant effect on the compressive strength, the flexural strength and the modulus of elasticity of the PC. Moreover, the PC made with recycled glass aggregate, MK and FA has good chemical resistance for 20% Na2CO3, 10% NaOH, tap water, and sea water. Besides the acceptable chemical resistance, the prepared waste glass PC shows low apparent porosity and low water absorption. [Copyright &y& Elsevier]

Abstract: This paper presents the findings of a long-term study on the mechanical and durability properties of concrete prepared with 0%, 50% and 100% recycled concrete aggregate that were cured in water or outdoor exposure conditions for 10years. The recycled aggregate concrete (RAC) was prepared by using 25%, 35% and 55% class-F fly ash, as cement replacements. It was found that, after 10years, the compressive strength and modulus of elasticity of the concrete prepared with 100% recycled concrete aggregate was still lower than that of the control concrete. Over this period, the highest gain in compressive strength and modulus of elasticity was recorded for the concrete mixture prepared with 55% fly ash. Fly ash improved the resistance to chloride ion penetration but it also increased the carbonation depth of the concrete. [Copyright &y& Elsevier]

Abstract: With rapid advances in the electronic industry, the management of cathode ray tube (CRT) glass waste has become a major environmental problem. In this study, 25% Ordinary Portland cement was replaced by Fly ash (FA) or Ground granulated blast-furnace slag (GGBFS), the crushed CRT funnel glass sand untreated with nitric acid (n-TFG) was used to replace river sand fine aggregate of 0%, 25%, 50%, 75% in the mortar. The fresh, mechanical properties of the mortar were studied, the alkali–silica reaction (ASR) expansion, drying shrinkage and leaching of lead from mortar were evaluated. The test results showed, the use of n-TFG glass sand improves fresh properties of the mortar. The mortar with n-TFG glass sand has higher mechanical properties than control mortar. At the drying shrinkage period of 56days, drying shrinkage of nearly all the mortar with n-TFG glass sand are higher than the limit of 0.075%. ASR expansion of the mortar are found to be below 0.1% at 14days tested age, except the mortar with GGBFS and 75% n-TFG glass sand. The lead leaching from mortar with n-TFG glass sand was reduced comparing the content of the leachable lead from n-TFG glass sand. Moreover, at a given replacement level of n-TFG glass sand, FA series mortar has better fresh properties, a lower wet density, mechanical properties, drying shrinkage, ASR expansion and the leaching of lead than GGBFS series mortar. [Copyright &y& Elsevier]

Abstract: The effects of replacement percentages and particle size distribution of recycled fine glass (FG) aggregates on the properties of dry–mixed concrete blocks were investigated. All the mixtures were proportioned with a fixed total aggregate/cement ratio of 4% and 50% of the total aggregate was fine aggregate. A total of 17 concrete block mixes, including a control (0% of glass) mix, were produced using four different particle sizes of FG (un-sieved, <2.36mm, <1.18mm and <600μm) as replacements of sand. The replacement ratios were 25%, 50%, 75% and 100%. Properties such as packing density, hardened density and water absorption, as well as the effects of air and water curing upon 7 and 28-day compressive strength were studied. The results show that the water demand of the mix increased with decreasing fineness modulus of the fine aggregate. All concrete blocks containing FG showed higher water absorption and lower hardened density than the control concrete block. For FG with particle size less than 600μm, this was more pronounced. Slight reductions in compressive strength were observed with the use of coarser FG, while significant increases in compressive strength occurred when the particle size of FG was reduced to less than 600μm. This indicates that finer FG exhibited appreciable pozzolanic reactivity. [Copyright &y& Elsevier]

Abstract: This paper presents the properties of concrete prepared with the sorted construction waste (low grade recycled aggregates) and a commercial recycled aggregate for concrete production. Three Series of concrete mixes were prepared by using the low grade or commercial recycled aggregates at 0%, 25%, 50% and 100% replacement levels of natural crushed granite. The concrete mixes were kept constant cement content and a free water to cement ratio of 410kg/m3 and 0.55, respectively. The test results on properties such as compressive and splitting tensile strength, E values, resistance to chloride-ion penetration and ultrasonic pulse velocity (UPV) are presented. The results showed that the strengths, E values and UPV of the concrete were decreased with an increase in the recycled aggregate content. The relationship between UPV and compressive strength was exponential for recycled aggregate concrete. Moreover, the recycled aggregate decreased the resistance to chloride ion penetration of the concrete. The results gathered would form a part of useful information for recycling the low grade recycled aggregates. [Copyright &y& Elsevier]

Abstract: The challenge of managing discarded cathode ray tube (CRT) waste has become a major environmental concern in Hong Kong and other cities. Recycled CRT funnel glass with a relatively high density (∼3000 kg m−3) can be used as a potential material for the production of heavyweight concrete. This paper presents the results of an investigation on the feasibility of using recycled CRT funnel glass, both treated (lead has been removed from the glass surface) and untreated (without removal of lead) as partial and full replacements of fine aggregates in heavyweight barite concrete. The inclusion of barite aggregate and recycled funnel glass increased the hardened density but reduced the compressive and splitting tensile strengths. The replacement of natural fine aggregate with recycled CRT glass had no significant effect on the elastic modulus but considerably improved the drying shrinkage of the concrete. In conclusion, the overall properties of heavyweight barite concrete made with the treated and untreated recycled CRT funnel glass are comparable, except for lead leaching results. The results show that it is feasible to use the treated CRT glass as 100% substitution of fine aggregate in making heavyweight concrete. However, the substitution of untreated glass should be limited to below 25% due to its potential lead leaching. [Copyright &y& Elsevier]

Abstract: The rapid development of the electronic industry has led to a growing hazardous waste management and disposal problem related to the management of cathode ray tube (CRT) waste. This study aimed to compare the feasibility of using CRT recycled glass: non-treated funnel glass (n-TFG, crushed without treatment) and treated funnel glass (TFG, crushed and treated with acid nitric to remove lead on the glass surface) as fine aggregates in cement mortar. Fresh and hardened properties of the cement mortars, including their x-ray radiation shielding and potential lead leaching were investigated. The mortar prepared with crushed beverage glass (CBG, lead-free) was also evaluated for comparison purposes. The experimental results show that the use of glass cullets, irrespective of glass type, improved the fluidity and drying shrinkage but reduced the strength. About 60% enhancement in x-ray radiation shielding property was achieved with the use of 100% CRT glass in the cement mortar owing to the increase of mortar density due to the presence of lead in the CRT glass. Furthermore, lead leaching (based on TCLP test) from the mortar samples prepared with the TFG complied with the regulatory limits. The results have demonstrated that the CRT glass (an original hazardous material) can be treated, processed, and re-utilized for making cement mortars. The mechanical performance of the cement mortar is comparable to that made with beverage glass. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to assess the performance of self-compacting glass concrete (SCGC) after exposure to four elevated temperatures of 300°C, 500°C, 600°C and 800°C. The influence of curing conditions on the high temperature performance of SCGC was also investigated. For each curing regime, five SCGC mixtures were prepared with recycled glass (RG) which was used to replace natural fine aggregate at the level of 0%, 25%, 50%, 75% and 100%. After exposure to the elevated temperatures, concrete mass loss, density, water porosity, ultrasonic pulse velocity (UPV) and water sorptivity were determined and then a compressive strength test was conducted. The test results indicate that regardless of the exposure temperature, all the water cured specimens had higher residual strengths and mass losses while the water porosity and water sorptivity values were lower as compared to the corresponding air cured specimens. The incorporation of RG in the concrete mixes helped to maintain the concrete properties after the high temperature exposure due to the melting and resolidification of the recycled glass in the concrete matrix. [Copyright &y& Elsevier]

Abstract: Recycled glass derived from cathode ray tubes (CRT) glass with a specific gravity of approximately 3.0g/cm3 can be potentially suitable to be used as fine aggregate for preparing cement mortars for X-ray radiation-shielding applications. In this work, the effects of using crushed glass derived from crushed CRT funnel glass (both acid washed and unwashed) and crushed ordinary beverage container glass at different replacement levels (0%, 25%, 50%, 75% and 100% by volume) of sand on the mechanical properties (strength and density) and radiation-shielding performance of the cement–sand mortars were studied. The results show that all the prepared mortars had compressive strength values greater than 30MPa which are suitable for most building applications based on ASTM C 270. The density and shielding performance of the mortar prepared with ordinary crushed (lead-free) glass was similar to the control mortar. However, a significant enhancement of radiation-shielding was achieved when the CRT glasses were used due to the presence of lead in the glass. In addition, the radiation shielding contribution of CRT glasses was more pronounced when the mortar was subject to a higher level of X-ray energy. [Copyright &y& Elsevier]

Abstract: This paper presents the results of a laboratory study on the performance of natural and recycled aggregate concrete prepared with the incorporation of different mineral admixtures including silica fumes (SF), metakaolin (MK), fly ash (FA) and Ground granulated blast slag (GGBS). The compressive and splitting tensile strength, drying shrinkage, chloride ion penetration and ultrasonic pulse velocity (UPV) of the concrete mixtures were determined. The test results, in general, showed that the incorporation of mineral admixtures improved the properties of the recycled aggregate concretes. SF and MK contributed to both the short and long-term properties of the concrete, whereas FA and GGBS showed their beneficial effect only after a relatively long curing time. As far as the compressive strength is concerned, the replacement of cement by 10% of SF or 15% of MK improved both mechanical and durability performance, while the replacement of cement by 35% FA or 55% GGBS decreased the compressive strength, but improved the durability properties of the recycled aggregate concretes. Moreover, the results show that the contributions of the mineral admixtures to performance improvement of the recycled aggregate concrete are higher than that to the natural aggregate concrete. [Copyright &y& Elsevier]

Abstract: The feasibility of using 100% recycled glass (RG) as a fine aggregate replacement in architectural white cement mortar was investigated. All the cement mortar mixtures were proportioned with a fixed water to binder ratio of 0.40. The dosage of superplasticizer was varied to produce highly workable recycled glass self-compacting white cement mortar (RG-SCWM) mixtures. Metakaolin (MK) was used in the RG-SCWM mixtures to suppress alkali-silica reaction (ASR). The test results revealed that increased in the recycled glass (RG) content improved the performance of workability and drying shrinkage. However, there was a gradual reduction in flexural and compressive strengths as the content of RG increased. The incorporation of MK effectively mitigated the ASR expansion and also increasing the resistance towards acid attack. Overall results have proved that it is feasible to produce aesthetically-pleasing architectural cement mortar by using 100% recycled glass as the fine aggregate. [Copyright &y& Elsevier]

Abstract: Rapid advances in the electronic industry led to an excessive amount of early disposal of older electronic devices such as computer monitors and old televisions (TV) before the end of their useful life. The management of cathode ray tubes (CRT), which have been a key component in computer monitors and TV sets, has become a major environmental problem worldwide. Therefore, there is a pressing need to develop sustainable alternative methods to manage hazardous CRT glass waste. This study assesses the feasibility of utilizing CRT glass as a substitute for natural aggregates in cement mortar. The CRT glass investigated was an acid-washed funnel glass of dismantled CRT from computer monitors and old TV sets. The mechanical properties of mortar mixes containing 0%, 25%, 50%, 75% and 100% of CRT glass were investigated. The potential of the alkali-silica reaction (ASR) and leachability of lead were also evaluated. The results confirmed that the properties of the mortar mixes prepared with CRT glass was similar to that of the control mortar using sand as fine aggregate, and displayed innocuous behaviour in the ASR expansion test. Incorporating CRT glass in cement mortar successfully prevented the leaching of lead. We conclude that it is feasible to utilize CRT glass in cement mortar production. [Copyright &y& Elsevier]